U.S. Steel's proposed $14.9 billion merger with Nippon Steel

(Corrects to add Timeline tag in headline, change dateline to Sept 5 from May 30)

(Reuters) -The White House is set to announce that President Joe Biden will block Nippon Steel's < 5401.T> $14.9 billion bid for the U.S. Steel citing national security concerns, two sources familiar with the situation told Reuters.

Nippon Steel agreed to acquire U.S. Steel last year, but has faced resistance since then from both an assertive labor union and the White House.

Here's a timeline of events leading up to the deal between the two steelmakers and the growing bipartisan political opposition:

Aug. 13, U.S. Steel announces aim to explore options